Add check-prefixes support for FileCheck. (#4769)

Merge from https://github.com/llvm/llvm-project/commit/fd557cb01f8ddf21202b3330f4d58d3c02912b72#diff-216ac5edd1cbc96da1241dc98b8d114529a874800aac4622871dbc99d16892d7

utils/FileCheck/FileCheck.cpp

@@ -52,6 +52,12 @@ static cl::list<std::string>
 CheckPrefixes("check-prefix",
               cl::desc("Prefix to use from check file (defaults to 'CHECK')"));
 
+static cl::alias CheckPrefixesAlias(
+    "check-prefixes", cl::aliasopt(CheckPrefixes), cl::CommaSeparated,
+    cl::NotHidden,
+    cl::desc(
+        "Alias for -check-prefix permitting multiple comma separated values"));
+
 static cl::opt<bool>
 NoCanonicalizeWhiteSpace("strict-whitespace",
               cl::desc("Do not treat all horizontal whitespace as equivalent"));